1. Field of the Invention
The present invention relates to transmission lines, and more particularly, to a transmission line driver for driving a transmission line.
2. Description of the Prior Art
With the advances in modern technology, human beings rely more and more on computer networks. Since many network applications (such as online multimedia applications) have strict bandwidth requirements, the bandwidth of some network devices has been upgraded from 10/100 Mbs to 1000 Mbs.
Under different transmission rates, a network device drives a transmission line by generating signals with different swing amplitudes. Generally speaking, under a low transmission rate (for example, 10 Mbs), signals with large swing amplitude should be used, hence a conventional network device will use a current mode to drive the transmission line. Under a high transmission rate (for example, 100/1000 Mbs), however, signals with low swing amplitude would be enough, and at this time a conventional network device will use a voltage mode to drive the transmission line.
FIG. 1 shows a schematic diagram of a conventional driver 100. The driver 100 shown in FIG. 1 drives a transmission line (represented by its equivalent impedance RL) through a transformer 50. Under a 10 Mbs transmission rate, the driver 100 operates under the current mode and a current driver 110 of the driver 100 generates current signals TXIP and TXIN to drive the transmission line. Under a 100/1000 Mbs transmission rate, the driver 100 operates under the voltage mode and a voltage driver 130 of the driver 100 generates voltage signals TXVP and TXVN to drive the transmission line. In the conventional driver 100 shown in FIG. 1, the current mode and the voltage mode operate in a mutually exclusive manner. Further more, the current driver 110 and the voltage driver 130 operate independent of each other.